The disclosure relates generally to building structures, and more particularly to shrinkage compensation devices for building structures having wooden frames.
In wood constructions, such as residences and smaller commercial buildings or hotels, the wood construction material naturally shrinks slightly over time. Shrinkage in lumber occurs as the moisture in the wood members evaporates causing the wood materials to constrict. Since only the wooden materials shrink (not fasteners or other metal components), the shrinkage of the building materials and the heavy load weight of building materials can result in an undesirable extra vertical clearance between levels and an overall loose structure. This phenomenon commonly causes the building to be susceptible to damage from uplift due to high winds or similar external forces. Thus, building compensation devices exist to restrain the building materials and prevent uplift. A typical system includes a series of elements: connectors at the roof to top of a wall, top of a wall to vertical studs, vertical studs between adjacent floors and to the foundation. In order to counteract upward loads from winds, the framing members may be anchored to the surface on which they are supported. On the ground level, anchor rods are typically sunk into a concrete foundation, and the bottom plate of the wall is bolted to the anchor rods. For levels built on top of the first level, straps or elongate fasteners are often used to anchor an upper level to the level below.
While effective at anchoring upper levels to lower levels, coil straps have certain drawbacks, including being positioned on the exterior of a framed construction, requiring alignment of vertical studs on adjacent floors Shrinkage in lumber occurs as the moisture in the wood members evaporates causing the members to constrict. This constriction may result in buckling or bowing outward of the strap, as well as any siding or exterior covering of the framed construction.
Compensation or take-up devices exist that allow a screw or similar elongate fastener to travel in one direction relative to a building level, while preventing the screw from traveling in the other direction exist for this reason. In practice, for example, a compensation device having a plate or similar element may be attached to the frame of an upper level of a building structure. An elongate fastener may be driven through the upper level frame with the distal end secured to the frame in the lower level. The compensation device in this example would allow the proximal end of the fastener (head) to travel upward relative to the top level frame, but prevent it from moving in the opposite direction.
Shrinkage compensation devices are shown and described in the art, including devices that mechanically engage with threads in the proximal portion of the elongate fastener to maintain the fastener with a ratchet engagement. Other devices exist that employ a torsion spring that biases two threaded members in opposite rotational directions so that the device can expand but not contract, or vice versa, depending on the position within the building frame structure. These known devices carry several drawbacks, including that the required firm mechanical metal-on-metal contact with the threads in the former example provides resistance in the direction of travel and can leave the threading vulnerable to stripping, as well as the strength of the ratchet engagement being limited by the shallowness of the threading. The rotationally biased devices can be prone to malfunction due to complexity and typically require several distinct steps during installation, making them inconvenient. Thus, there is a need for a building shrinkage compensation device that is easy to install and reduces or omits all of the aforementioned drawbacks.